The present invention relates to a recording and/or reproducing technique for PCM signals, and in particular to a PCM signal recording and/or reproducing method and apparatus suitable for recording and/or reproducing audio PCM signals onto and/or from a digital audio tape recorder (hereafter referred to as DAT).
The DAT for converting an audio signal into PCM signals and recording the PCM signals onto a magnetic tape is excellent in tone quality and free from quality deterioration caused by the recording and reproducing operation.
A technical trend in the development of the rotary-head type digital audio tape recorder (hereafter referred to as R-DAT) is described in "DAT Meeting Activity" on pages 36-42, particularly pages 40-42 of ELECTRONICS, vol. 24, No. 10, 1984 published by EIAJ (Electronics Industries Association of Japan).
As described on page 40 of the above described literature, the first PCM signal having a sampling frequency of 48 KHz, a quantization of 16 bits per sample, and two channels 2 (left and right) was recorded onto tape as an experimental format of the R-DAT. The first PCM signal corresponds to the B-mode specification in the PCM signal transmission of the satellite broadcast in Japan.
FIG. 2 shows a record pattern on the magnetic tape of the R-DAT described on page 41 of the aforementioned literature. On the magnetic tape 33, blocks of the above described first PCM signal are recorded alternately on a plus azimuth track 34 and on a minus azimuth track 35. The head gaps of heads 32a and 32b shown in FIG. 1 are slanted with respect to a face perpendicular to the record direction as indicated by oblique lines of FIG. 2. Accordingly, the first PCM signal is also recorded in the directions indicated by oblique lines of FIG. 2. These tracks are referred to as azimuth tracks. The terms "plus azimuth" and "minus aximuth" mean that the oblique directions of tracks 34 and 35 are opposite each other as illustrated by oblique lines.
FIGS. 3 and 4 show the configuration of an example of PCM data recorded on respective tracks of FIG. 2. FIG. 3 shows the data arrangement on the plus azimuth track 34 of FIG. 2. FIG. 4 shows the data arrangement on the minus aximuth track 35 of FIG. 2. Numeral 36 denotes one symbol unit which consists of 8 bits. Usually, one-word signal comprises two symbols, an upper symbol and a lower symbol. One block comprises 32 symbols and 128 blocks are recorded on one track. Numeral 38 denotes a first error detection and correction code Q and numeral 37 denotes a second error detection and correction code P. Letter L represents left channel data and letter R represents right channel data. The suffix following L or R represents a serial number of the left channel data or right channel data. The suffix 0, 2, 4, . . . represents even-numbered data and the suffix 1, 3, 5, . . . represents odd-numbered data. Letter U represents the above described upper symbol and letter l represents the above described lower symbol.
Data dispersion is conducted in data recording so that error compensation may be effected by means of mean value interpolation even if a large burst error occurs in data reproduction. That is to say, even-numbered data of the left channel is recorded on former halves of plus azimuth tracks and odd-numbered data of the left channel is recorded on latter halves of minus azimuth tracks. Similarly even-numbered data of the right channel is recorded on former halves of minus azimuth tracks and odd-numbered data of the right channel is recorded on latter halves of plus azimuth tracks. Examples of this arrangement will now be described by referring to FIGS. 3 and 4. Even-numbered data Lou of the left channel is indicated on block No. 0 of FIG. 3. This fact means that the data Lou is recorded on the former half of the plus azimuth track 34 of FIG. 2 with respect to the record direction. Data L1u following the data Lou is indicated on block No. 76 of FIG. 4. This fact means that the data L1u is recorded on the latter half of the minus azimuth track 35 with respect to the record direction. The even-numbered data Lou of the left channel and the even-numbered data Ro1 of the right channel corresponding thereto are disposed on the same block number 0 at an interval of one symbol. Since the sampling frequency is 48 KHz and the number of rotations of the cylinder is 2,000 rpm in the rotary-head type DAT, data of 5760 symbols are recorded on two tracks.
In an R-DAT, the data arrangement was so designed that the first PCM signal having a sampling frequency of 48 KHz, a quantization of 16 bits per sample, and the two channels (left and right) would be optimally recorded. However, practical consideration was not given to the recording arrangement for the second PCM signal which is different from the above described PCM signal in sampling frequency, the number of quantized bits per sample, and the number of channels. An example of the second PCM signal source corresponds to the A-mode specification in the PCM signal transmission of the satellite broadcast in Japan.